ARLINGTON, Va.  Raise your hand if you've heard of "Second Life," police Lt. Charles Cohen asks a room of about 75 law enforcement officers from around the country. "Second Life," a sprawling online universe, has had technology circles abuzz for a while. But here, it might as well be a watch repair shop. Only a few hands go up. Cohen has some explaining to do.

And so begins another session in the traveling classroom of this fast-talking Indiana state trooper at the forefront of the idea that cops need to be better at incorporating the online world into their patrols.

Many police departments have computer crews that perform skillful forensic analysis on hard drives and specialize in nailing online predators. Cohen's lectures are not for them.

Instead he's trying to reach everyone else in law enforcement: beat cops, homicide detectives and other investigators who might otherwise think monitoring the Internet is not their responsibility.

More and more, such boundaries don't make sense. Whether it's on MySpace, Facebook, "Second Life" or other Web flavors of the moment, criminals and victims -- especially young ones -- are leaving clues in plain sight online, even for offline crimes. Things people once wrote in private diaries now cascade through Web sites that stimulate free expression -- and are open to anyone who comes looking.

In one recent example, a detective in Newark, N.J., tracked the alleged killers of three college students by mining MySpace pages maintained by the suspects and their friends. In another, pictures and prose posted online by the killer of Taylor Behl, a 17-year-old Virginia college freshman, connected him to the victim and ended up revealing where her body was stashed.

And in an Indiana case in which Cohen helped, a young man wrote on his MySpace page: "I just killed two cops." (One officer survived the shooting.)

"People under 25 tend to think about what is public versus private information differently from the rest of us, and that is great for law enforcement investigators," Cohen, 37, tells his audience in Arlington, at a conference of the National White Collar Crime Center. Later, he adds in an interview, "Your computer usage is in some ways a window into your soul."

But the anonymity and the sheer scope of the Internet also can make it easier for criminals to cover their tracks. And today's hot online hangout is tomorrow's dead zone. The trick for cops is to figure out how to keep up -- a proactive step that doesn't come easy, given that most police departments have to concentrate their limited resources on reacting to crimes.

Les Lauziere, a computer crimes investigator for the Virginia Attorney General who was part of the Behl case, suggests that police need to incorporate Internet analysis into just about every investigation. In the coming years, he says, asking whether a police department has a distinct cybercrime unit will be like asking if there's a telephone squad.

Steven DeBrota, a federal prosecutor in Indiana, argues that too much separation between cyber-specialists and other cops can be dangerous.

Typically, he says, detectives will transfer a suspect's computer to forensic examiners who might need months to produce a full report on the contents, especially with hard drives ballooning to monumental sizes. In that time, DeBrota fears, the opportunity to find a suspect's associates or additional victims may be lost.

So DeBrota has pushed an alternative approach in Indiana. Now computer specialists get out of their labs and assist detectives on sweeps and arrests. At the same time, front-line cops have been trained to do some of the basics. They can take hard drives out of computers, attach "write-blocking" clips that prevent data from being altered, and then do initial, targeted searches for evidence -- Google searches typed, videos watched -- that might be valuable in interrogations.

For all the logic of this approach, it is far from common. At best, several departments have launched profiles on social-networking sites like MySpace, so people can report tips or informally chat with cops.

"Not everyone watches the news at night. Not everyone reads the paper. Not everyone even reads news online. But it seems like everyone is on MySpace," says Stephanie Slater, a police spokeswoman in Boynton Beach, Fla. Her department's MySpace page gets more hits than its general Web site does.

Yet for all that MySpace reveals in its 200 million profiles, it's just one of innumerable online avenues. Spending some time in Cohen's class shows just how hard it is to track them all.

He suggests ways to hunt for clues not only on obvious social-networking zones like Facebook and MySpace but also the likes of Xanga, Bebo and Orkut. Given that people often don't use their real names online, cops might have to ask friends of suspects and victims not only where they hung out in the physical world, but also which Web sites they frequented.

The answers likely go beyond social-networking sites. People jabber in "Second Life" or through chat programs in online games like "Runescape" or "World of Warcraft." Sometimes they don't say much but show a lot on real-time Web video sites like Stickam.

Each of those sites has different procedures required of law enforcement agents who want to match anonymous user names with the Internet Protocol address behind them. Then more work is needed to ask an Internet service provider to cough up the IP address holder's real name and address, assuming it wasn't a cybercafe or library.

Investigators say most sites are extremely cooperative with subpoenas, warrants and other requests for help. In particular, MySpace, owned by Rupert Murdoch's News Corp., has a former federal prosecutor as its head of security and maintains valuable logs on site activity for at least 90 days. Some sites maintain such logs for much less time, if at all.

To listen to Cohen is to walk through dark corners of the Internet. There are gang members boasting on MySpace, killers revealing their obsessions on LiveJournal, teenagers sharing drug-making tips on YouTube, prostitutes hawking themselves on Craigslist, child pornography flourishing on Internet Relay Chat, a specialists' slice of the Internet separate from the Web.

Yet Cohen, in a cop's matter-of-fact manner, is measured in his approach.

"Social networks are not a bad thing. It's a great thing," he says. "It's like any community, communities we all live in. There are going to be criminals in it."

Cohen began his career with the Indiana State Police like any other trooper, writing speeding tickets and responding to accidents. Eventually he moved into complex fraud and corruption cases, and found that increasingly his work had an online component. But hardly anyone was available to coach him. So he mainly taught himself, with help from tech blogs and news stories.

Now he spends most of his vacation time and a few of his state police hours relaying what he's learned to local, state and federal agencies. At the recent three-day conference of the National White Collar Crime Center, Cohen's presentation was in such demand that it was the only one offered twice.

At one session, Cohen's audience nods along as he shows how officers can plumb public pages of social-networking sites to get to know people's likes, dislikes, friends and hobbies before questioning them in an investigation.

But his pupils have trouble accepting the particulars of "Second Life," where people chat, shop, trade stuff and have sex -- and in Cohen's estimation, launder money occasionally -- through animated characters known as avatars.

"Is this for people who don't want social contact?" one investigator asks.

Cohen shakes his head as if to say it's not that simple.

"This," he says, "is our new world."

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Indiana State Police officer Lt. Charles Cohen poses by a squad car in Indianapolis, Wednesday, Oct. 31, 2007. This fast-talking Indiana state trooper is at the forefront of an important movement in policing